Method for Producing Wrought Aluminum Articles Having a Colored Anodic Oxidation Film

ABSTRACT

This invention relates to a method for producing a wrought aluminum article having a colored anodic oxidation film wherein an aluminum article which always has a uniformly colored film and which has higher reproducibility can be obtained. The film obtained shows a characteristic grayish pale silvery color and has a wide range of application.

Mizukami et al.

METHOD FOR PRODUCING WROUGHT ALUMINUM ARTICLES HAVING A COLORED ANODIC OXIDATION FILM Inventors: Ichiro Mizukami; Masahiro Takahasi, both of Shimizu, Japan Assignee: Nippon Light Metal Research I Laboratory Limited, Tokyo, Japan Filed: July 19, 1973 Appl. No.: 380,696

Related U.S. Application Data Continuation of Set. Nov 211,041, Dec. 22, 1971.

Foreign Application Priority Data Feb. 4, 1975 [56] References Cited UNITED STATES PATENTS 2,941,930 6/1960 Mostovych et al. 204/29 2,998,358 8/1961 Nakayama 204/29 3,180,806 4/1965 Hollingsworth 204/29 3,351,442 11/1967 Hooper 29/1835 Primary Examiner-John H. Mack Assistant Examiner-Aaron Weisstuch Attorney, Agent, or Firm-William J. Daniel [57] ABSTRACT This invention relates to a method for producing a wrought aluminum article having a colored anodic oxidation film wherein an aluminum article which always has a uniformly colored film and which has higher reproducibility can be obtained. The film obtained shows a characteristic grayish pale silvery color and has a wide range of application.

7 Claims, No Drawings METHOD FOR PRODUCING WROUGI-IT ALUMINUM ARTICLES HAVING A COLORED ANODIC OXIDATION FILM This is a continuation, of Ser. No. 2] 1,041, filed Dec. 22, i971.

This invention relates to a method for producing wrought aluminum articles having a grayish pale silvery anodic oxidation film.

A method has been proposed previously for producing an aluminum article having an anodic oxidation film, called a self-coloring anodic film, of any tone, by anodically oxidizing an aluminum material to which a color developing alloying element has been added. In such a conventional self-coloring anodic film process, there is a possibility of difference in the tone of the colored film in the various lots produced and a partial color irregularity due to difference-in the amount of additive element or treating condition. The present invention is a method for producing wrought aluminum articles having an anodic oxidation film which has a characteristic elegant color, higher reproducibility than any conventional color developing films, and less color irregularities.

It is therefore, an object of the present invention to provide a method for producing a wrought aluminum article having a colored anodic film, particularly having a characteristic grayish pale silvery colored anodic film.

Another object of the present invention is to provide a method for producing with high reproducibility wrought aluminum article having uniformly colored anodic films.

In accordance with the present invention, a uniform grayish pale silvery colored wrought aluminum article is produced by anodically oxidizing a wrought aluminum article containing about 1 to 3 percent iron and less than 0.2 percent silicon after carrying out a heattreatment of the wrought aluminum article, or an intermediate worked product, or the initial casting body at a higher temperature than in the usual annealing treatment.

Thus, the method of the present invention for producing a wrought aluminum article having a grayish pale silvery anodic oxidation film includes the steps of working such cast aluminum body containing 1.0 to 3.0 percent iron and less than 0.2 percent silicon, anodically oxidizing the above mentioned wrought aluminum article and heat-treating the casting body or the aluminum article while or after working the casting body.

The method of the present invention is described in further detail below.

The aluminum alloy to be used in the present invention contains 1.0 to 3.0 percent iron and less than 0.2 percent silicon. When the content of iron is less than the lower limit of 1.0 percent, the characteristic color of the present invention will be not obtained. When the content of iron is higher than the upper limit of 3.0 percent, films with non-uniform color will be produced. It is preferable to have the silicon content higher than 0.02 percent. However, when the upper limit of 0.2 percent silicon is exceeded, the film will tend to be yellowish, which is not desirable. When the content of silicon is less than 0.02 percent, the surface of the film will be lustrous and the characteristic elegant color of the present invention will be impaired. An aluminum melt having the abovementioned iron and silicon contents is cast in the form of a slab or billet preferably by a metallic mold or water-cooled casting method.

The cast body thus obtained is worked in an ordinary manner, such as rolling, extruding, forging and pressing. That is, when a plate is to be produced, the casting body is wrought by hot and/or cold rolling.

In the method of the present invention, the initial cast body or an intermediate stage or final wrought article is heat-treated at a temperature of above 550C. This heating temperature is higher than the ordinary annealing temperature for the aluminum material in the working step. The heating time of the heat-treatment step depends on the heating temperature and the content of iron in aluminum. When the heating temperature is low or the content of iron is high, heating for a longer time will be required. As a result of experiments, more than 2 hours were required when heating at 600C., in case of iron content of 1.0 percent and more than 12 hours in the case its content was 3.0 percent. When the heating temperature is low or the heating time insufficient, the film obtained by the anodic oxidation will be grayish black.

After heat-treatment, the wrought aluminum article is anodically oxidized to produce a colored film on its surface.

In the anodic oxidation, when an aqueous solution of sulfuric acid is used for the electrolyte, an anodic film of a grayish pale silvery color will be obtained. lt is preferable to use a current density less than 2 amp./dm When the current density exceeds 2 amp./dm the film will be yellowish. The pore sealing treatment of the anodically oxidized film is carried out according to the conventional method.

As can be seen from the above description, according to the present invention an elegant grayish pale silvery colored aluminum article can be obtained with high uniformity and high reproducibility. Therefore, the wide range of application such as a material for inside and outside fittings of buildings, furniture and kitchen utensils will be expected to the product of the present invention.

EXAMPLE 1 An aluminum melt (containing 0.1% Si) to which 1.8% Fe had been added was cast into a slab of 50 mm. by using a metallic mold. This slab was hot-rolled at 450C. to a thickness of 6 mm. The coil thus obtained was heated at 600C. for 8 hours and after cooling, it was cold-rolled to a thickness of 0.5mm. The plate thus obtained was anodically oxidized under the electrolyzing conditions of a temperature of 2l-OC. and a current density of l am./dm by using sulfuric acid of a concentration of 15 percent as the electrolyte and was then dipped in hot water at 98C. to seal the pores. An aluminum article having a light grayish pale silvery film was obtained.

EXAMPLE 2 An aluminum melt (containing 0.1% Si) to which 1.5% Fe had been added was cast by the continuous water-cooled-casting process into a slab of a thickness of 50mm. This slab was heated at a temperature of 600C. for 3 hours and was hot-and-cold-rolled to a thickness of 0.5mm. The plate thus obtained was anodically oxidized in the same manner as in Example I. An

, aluminum article having a light grayish pale silvery film was obtained.

EXAMPLE 3 An aluminum melt (containing 0.03% Si) to which 2.0% Fe had been added was cast by the water-cooledcasting process into a billet of a diameter of 100mm. This billet was extruded into a shape at a temperature of 400C. and then heated at 600C. for hours. After cooling, the shape thus obtained was anodically oxidized the same manner as in Example 1. An aluminum article having a light grayish pale silvery film was obtained.

What is claimed is:

l. A method for producing a wrought aluminum article having a pale silvery colored anodic oxidation film which comprises the steps of casting a body of an aluminum alloy containing about 1-3 percent by weight of iron and about 0.02 to less than about 0.2 percent by weight'of silicon, with the balance aluminum, working said cast aluminum body into a wrought aluminum article, anodically oxidizing the thus obtained wrought aluminum article in an aqueous electrolyte consisting of sulfuric acid within a concentration range of about 10-20 percent at anodizing current density less than 2 'cally oxidizing step, heat-treating said article at a temperature of above about 550C but insufficient to alter the shape of the article.

2. The method of claim 1 wherein said cast body is worked by rolling.

3. The method of claim 1 wherein said cast body is worked by extrusion.

4. The method of claim 1 wherein said working step is carried out in plural stages and said heat-treatment is effected between two of such stages.

5. The method of claim 1 wherein said cast body is heat-treated before working.

6. The method of claim 1 wherein said heattreatment was for a period of at least 2 hours and inr creasing with increasing content of iron in said alumithereon. 

2. The method of claim 1 wherein said cast body is worked by rolling.
 3. The method of claim 1 wherein said cast body is worked by extrusion.
 4. The method of claim 1 wherein said working step is carried out in plural stages and said heat-treatment is effected between two of such stages.
 5. The method of claim 1 wherein said cast body is heat-treated before working.
 6. The method of claim 1 wherein said heat-treatment was for a period of at least 2 hours and increasing with increasing content of iron in said aluminum body.
 7. The method of claim 1 including the step of immersing the anodically oxidized aluminum article into hot water in order to seal the anodic oxidation film thereon. 